What does 'glossing' hair mean?

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Is it a permanent thing or more like a deep conditioning? Have seen it mentioned a few times - sounds like something I would like - hair highlighted 'natural' blondish but quite dull. Can you have it done over highlights? Ta!

It's like a semi-permanent clear coating that they apply like a colour , adds gloss over whatever colour you have and washes out after a certain amount of shampoos. I used it get it over my dark all over colour.

Thanks thought, was there a noticeable difference?